December 2020 - kernelnewbies@kernelnewbies.org

Why new kernel version cannot be installed on old Ubuntu?
by Joontaek Oh Dec. 5, 2020

Dec. 5, 2020

Dear kernelnewbies mailing system. Hello, I am a student studying the Linux kernel. I mostly use the Linux kernel version 3.10.61 or 4.18.0, and Ubuntu for the Linux distribution. However, version 3.10.61 is not installed on the late Ubuntu version (18.04), while version 4.18.0 is not installed on the old Ubuntu version (14.04). So, I am using my laptop with the multi-booting but it is too space-consuming. Moreover, I get work that needs to modify the kernel 3.10.0 for Centos, but the kernel 3.10.0 is not installed on the Ubuntu any version, and the kernel 3.10.61 or the kernel 4.18.0 is not installed on Centos. So, I have to install three Operating System on my laptop. I tried to install them on a single OS among Ubuntu 14.04, 16.04, 18.04, and Centos7.4, but I failed, being hung up during booting. If you know why the problem occurs and how can it be solved, could reply me? Sincerely. Joontaek Oh.

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hot take question for the day
by jim.cromie＠gmail.com Dec. 4, 2020

Dec. 4, 2020

so I was looking at the following code, from dynamic_debug.c, I saw a minor code optimization, and wondered whether its already optimized away by compiler. Instead of actually testing it ( I intend to eventually ) I figure Id ask if you all want to take an educated guess ? or perhaps just do the test, and post results. And since Im making a game of it, I might suggest a prize - that by prepping a patch, showing its effect (none? tiny? not observable in objdump?) and submitting it, I would ack it I suspect that Greg might take it ; its a legit sub-optimality and fix is at least decluttering and deobfuscating. so heres the snippet. if you got this far, you can find the prob (or 2) static char *dynamic_emit_prefix(struct _ddebug *dp, char *buf) { int pos_after_tid; int pos = 0; *buf = '\0'; if (dp->flags & _DPRINTK_FLAGS_INCL_TID) { if (in_interrupt()) pos += snprintf(buf + pos, remaining(pos), "<intr> "); else pos += snprintf(buf + pos, remaining(pos), "[%d] ", task_pid_vnr(current)); }

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Configuring kdump for ARM64
by Pankaj Vinadrao Joshi Dec. 3, 2020

Dec. 3, 2020

Hi, i am trying to configure kdump for my ARM64 with custom kernel(5.8) also i have compiled my kernel with all configs required for kdump and kexec. I have tried to with the help of google but didn't worth since all i have is x86. Can someone help me to do it ?? Thanks

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